Illumination apparatus for display device, display device using the same, and television receiver apparatus comprising the display device

ABSTRACT

In a backlight apparatus, laminated optical sheets are housed in a tray such that a wall portion thereof surrounds their circumferences so that the optical sheets receive light from fluorescent lights. Tips of one corner portion A of optical sheets preferably have a shape in which the tips are trimmed by line segments extending between two edges defining the corner portions. At the wall portion of the tray, an opposing surface is formed along the line segments of the corner portions so as to correspond to the shape of the corner portions having tips trimmed off. The opposing surface restrains the line segments.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illumination apparatus for a displaydevice used in a liquid crystal panel or the like, a display deviceincluding the same, and a television receiver apparatus including thedisplay device.

2. Description of the Related Art

Japanese Patent Laid-Open No. 2000-11728 (FIG. 1) describes aconventional device relating to a backlight apparatus for a liquidcrystal display device. In that device, a plurality of optical sheetsare laminated and disposed so as to face a light source housing portion,such that light emitted from the light source is uniformly radiated ontoa display by the optical sheets.

In some cases, optical sheets that have directionality with respect tothe top and bottom surfaces are included among the plurality of opticalsheets. If an optical sheet of this kind is mistakenly disposed with thetop and bottom surfaces on the opposite sides, correct illuminationcannot be performed for the display and a display device that uses thatillumination apparatus will be unable to properly display an image.

According to the prior art as described in Japanese Patent Laid-Open No.2000-11728, an ear portion is caused to protrude from one edge of eachoptical sheet, and the ear portions are formed at respectively differentpositions among the optical sheets. Therefore, since the positions ofthe ear portions will be irregular when any of the optical sheets aremistakenly disposed with their top and bottom surfaces inverted, it ispossible to easily discover that the top and bottom surfaces aremistakenly disposed.

However, according to the above described prior art, because the earportions protrude from the optical sheets, the size of a housing thatstores the optical sheets is increased by the size of the ear portionsand the size of the overall illumination apparatus thus increases. Inorder to reduce the size of the apparatus, it is necessary to reduce theexternal shape of the optical sheets, but if the optical sheets areprovided with the ear portions as they are, the active area of theoptical sheets will be decreased.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide an illumination apparatus for a displaydevice that makes it possible to easily discover when the top and bottomsurfaces of optical sheets are disposed in an inverted state, and alsohas a small size, as well as a display device that includes such anillumination apparatus, and a television receiver apparatus includingsuch a display device.

According to a preferred embodiment of the present invention, anillumination apparatus for a display device includes an optical sheethaving a plurality of corner portions and housed in a housing in acondition such that a wall portion thereof surrounds the circumferenceof the optical sheet so that the optical sheet receives light from alight source in the housing, wherein a tip of at least one of the cornerportions of the optical sheet has a shape in which the tip is trimmed bya line segment extending between two edges that define the cornerportion, at the wall portion of the housing an opposing surface isarranged along the line segment of the corner portion so as tocorrespond to the shape of the corner portion at which the tip istrimmed, and when the optical sheet is housed in the housing in a statein which the top surface and the bottom surface thereof are inverted,one of the other corner portions thereof is disposed at an area at whichthe opposing surface of the housing is provided and comes to astandstill on the opposing surface.

Thus, since one of the corner portions comes to a standstill on theopposing surface, it is possible to easily discover that the opticalsheet is disposed in an upside-down condition. Further, since theconfiguration is one in which only the tip of a corner portion of theoptical sheet is trimmed off, it is possible to make a smallillumination apparatus without sacrificing the active area of theoptical sheet.

In this connection, the aforementioned housing also includes a housingcomprising a plurality of components that use a material such as metalor synthetic resin, and is not limited to a concept of only a housingformed with a single component.

The following configurations are preferable as various preferredembodiments of the present invention.

An illumination apparatus for a display device includes a plurality ofoptical sheets which are laminated and housed in a housing, tips of atleast one corner portion of the optical sheets define a sheet inversiondetection portion by being formed in a similar shape in which the tipsare trimmed by the line segment so as to follow an opposing surface ofthe housing, at least one tip of the other corner portions has a shapein which the tip is trimmed by a second line segment that extendsbetween two edges that define the corner portion such that these cornerportions define a missing sheet detection portion by being stacked inorder from the corner portion with the largest remaining area, and whenthe optical sheets are housed in the housing in a state in which the topsurface and the bottom surface are inverted, the missing sheet detectionportion is disposed at an area at which the opposing surface of thehousing is provided and comes to a standstill on the opposing surface.

Therefore, the sheet inversion detection portion makes it easy todiscover that an optical sheet is disposed in an upside-down condition,and the missing sheet detection portion makes it easy to discover thatan optical sheet is missing among a plurality of optical sheets.

In this connection, the term “similar shape” described above refers to ashape that corresponds to the opposing surface of the housing, and is aconcept that includes slight differences in shape and dimensions withinthe scope thereof.

Each of the optical sheets preferably has a substantially rectangularshape, a pair of the sheet inversion detection portions are provided atdiagonally opposing corner portions of the optical sheets, and themissing sheet detection portion is provided at one of the remainingcorner portions so that, by checking corner portions at a minimum of twoadjacent positions, it is possible to discover that an optical sheet isdisposed in an upside-down condition and, further, such a check can beeasily carried out in a short time.

Each of the optical sheets preferably has a substantially rectangularshape, a pair of the missing sheet detection portions are provided atdiagonally opposing corner portions of the optical sheets, and the sheetinversion detection portion is provided at one of the remaining cornerportions so that, by checking corner portions at a minimum of twoadjacent positions, it is possible to discover that there is a missingoptical sheet and, further, such a check can be easily carried out in ashort time.

Each of the optical sheets preferably has a substantially rectangularshape, a pair of the sheet inversion detection portions are provided atdiagonally opposing corner portions of the optical sheets and a pair ofthe missing sheet detection portions are provided at the remainingcorner portions so that, by checking corner portions at a minimum of twoadjacent positions, it is possible to discover that an optical sheet isdisposed in an upside-down condition or is missing and, further, thesechecks can be easily carried out in a short time.

Each of the optical sheets preferably has a substantially rectangularshape, and one sheet inversion detection portion and one missing sheetdetection portion are provided at corner portions that oppose each otheron a single diagonal line so that, when forming the optical sheets bycutting off corner portions of a sheet member that has a substantiallyrectangular shape, the cutting areas can be reduced to enablefabrication in a short time.

Each of the optical sheets preferably has a substantially rectangularshape, and missing sheet detection portions are provided at three cornerportions among the four corner portions and a sheet inversion detectionportion is provided at the remaining one corner portion so thatdetection of a missing optical sheet among the optical sheets can besurely carried out at the three missing sheet detection portions.

Each of the optical sheets preferably has a substantially rectangularshape, and sheet inversion detection portions are provided at threecorner portions among the four corner portions and a missing sheetdetection portion is provided at the remaining one corner portion sothat it is possible to surely detect that an optical sheet is disposedin an upside-down condition at the three sheet inversion detectionportions.

At the missing sheet detection portion, an optical sheet in which twoedges that define a corner portion are joined by an arc so as to projectoutward, is stacked on an optical sheet in which two edges that define acorner portion are joined by a straight line and, further, an opticalsheet in which the two edges that define a corner portion are joined bya straight line is stacked thereon and edge portions of the arc are atpositions which are linked by the straight line of the optical sheetthat is stacked thereon so that, even when three sheets are placed ontop of each other, the arc and the straight line of the optical sheetstacked thereon do not overlap, and thus these can be clearlydistinguished. Further, since the straight line of the optical sheetlocated at the uppermost layer is not provided in a condition in whichit is separated from the arc and penetrates deeply towards the innerside, and the sectional width thereof does not become large, it ispossible to make the illumination apparatus for a display device smalland lightweight.

By forming an optical sheet by cutting off a corner portion of a sheetmember that preferably has a substantially rectangular shape, a normalsheet member that has a substantially rectangular shape that is used formultiple purposes can be used as the raw material of the optical sheet,enabling provision of the optical sheet at a low cost.

By forming an optical sheet to have a shape in which a corner portion istrimmed off using a forming die, the optical sheet can be fabricated byonly a forming process, without cutting or the like.

By disposing a display in front of the above described illuminationapparatus for a display device, it is possible to make a small displaydevice for which it is easy to discover that an optical sheet isdisposed in an upside-down condition.

By adopting a configuration that includes the above described displaydevice, it is possible to provide a small television receiver apparatusin which it is easy to discover that an optical sheet is disposed in anupside-down condition.

Since it is possible to easily discover that an optical sheet isdisposed in an upside-down condition, the workability with respect tofabrication is improved and a low cost illumination apparatus for adisplay device can be provided.

Additional elements, characteristics, steps, features, and strengths ofthe present invention will be made clear by the description below.Further, the advantages of the present invention will be evident fromthe following explanation in reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a television receiverapparatus according to a preferred embodiment of the present invention.

FIG. 2 is an exploded perspective view of a liquid crystal display shownin FIG. 1.

FIG. 3 is a plan view of an optical sheet shown in FIG. 1.

FIG. 4A is an exploded plan view of a state before sheet inversiondetection portions of optical sheets are housed in a tray.

FIG. 4B is an enlarged plan view showing a state when sheet inversiondetection portions of the optical sheets are housed in the tray.

FIG. 5A is an exploded plan view of a state before missing sheetdetection portions of optical sheets are housed in a tray.

FIG. 5B is an enlarged plan view showing a state when missing sheetdetection portions of the optical sheets are housed in the tray.

FIG. 6A is an enlarged plan view showing a state when a top surface anda bottom surface of a light guide plate are disposed in an invertedstate such that a missing sheet detection portion comes to a standstillon an opposing surface of the tray.

FIG. 6B is an enlarged plan view showing a state when a top surface anda bottom surface of a diffusing sheet are disposed in an inverted statesuch that a missing sheet detection portion comes to a standstill on anopposing surface of the tray.

FIG. 6C is an enlarged plan view showing a state when a top surface anda bottom surface of a lens sheet located on the lower side are disposedin an inverted state such that a missing sheet detection portion comesto a standstill on an opposing surface of the tray.

FIG. 6D is an enlarged plan view showing a state when a top surface anda bottom surface of a lens sheet located on the upper side are disposedin an inverted state such that a missing sheet detection portion comesto a standstill on an opposing surface of the tray.

FIG. 7 is an exploded cross-sectional view showing a state when a topsurface and a bottom surface of an optical sheet is disposed in aninverted state.

FIG. 8A is a plan view of an optical sheet according to modificationexample 1 of a preferred embodiment of the present invention.

FIG. 8B is a plan view of an optical sheet according to modificationexample 2 of a preferred embodiment of the present invention.

FIG. 8C is a plan view of an optical sheet according to modificationexample 3 of a preferred embodiment of the present invention.

FIG. 8D is a plan view of an optical sheet according to modificationexample 4 of a preferred embodiment of the present invention.

FIG. 8E is a plan view of an optical sheet according to modificationexample 5 of a preferred embodiment of the present invention.

FIG. 8F is a plan view of an optical sheet according to modificationexample 6 of a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be describedreferring to FIG. 1 to FIG. 7. A television receiver apparatus 1according to the present preferred embodiment preferably includes aliquid crystal display 2, a tuner circuit 5, a housing case 6 thathouses these elements, a cabinet 7 that is mounted at the front surfaceof the liquid crystal display 2, and a stand 8 that supports the housingcase 6 from below (see FIG. 1). The liquid crystal display 2 correspondsto the display device according to various preferred embodiments of thepresent invention and preferably includes a backlight apparatus 3(corresponding to the illumination apparatus for a display device of thepresent invention) and a display panel 4 that is disposed at the frontthereof and can display images (corresponding to the display of thepresent invention) (see FIG. 2).

The display panel 4 preferably includes a pair of glass substrates 42that are fitted inside frames 41, respectively, a pair of transparentelectrodes mounted therebetween, and a panel substrate 43 including anorientation film including liquid crystal. The backlight apparatus 3preferably is an apparatus referred to as a “direct-type backlightapparatus” that includes a tray 32 (corresponding to the housing of thepresent invention) that houses a plurality of fluorescent lights 31(corresponding to the light source of the present invention), a lightguide plate 33 that is disposed directly above the tray 32, a diffusingsheet 34 that is disposed directly above the light guide plate 33, andtwo lens sheets 35 and 36 that are disposed above the diffusing sheet34, although the backlight apparatus is not limited thereto. The lightguide plate 33, the diffusing sheet 34, and the lens sheets 35 and 36are preferably formed of a synthetic resin and correspond to the opticalsheets of the present invention. As shown in FIG. 2, because each ofthese optical sheets has four corner portions, these sheets preferablyhave a substantially rectangular shape when viewed from above.

As shown in FIG. 2, a reflection sheet 32 a is provided inside the tray32, and the plurality of fluorescent lights 31 are positioned on thereflection sheet 32 a. Each fluorescent light 31 is disposed in parallelor substantially in parallel at equal distances inside the tray 32, andpreferably have an overall planar shape. The laminated light guide plate33, diffusing sheet 34, and lens sheets 35 and 36 are arranged such thattheir peripheries are surrounded inside the tray 32 by a substantiallyrectangular wall portion 32 b thereof so as to receive light from thefluorescent lights 31, and are housed such that their positions arerestricted (see FIG. 2, FIG. 4, and FIG. 5).

A tip of one corner portion (denoted by reference character A in FIG. 3)at the same location in the laminated light guide plate 33, thediffusing sheet 34 and the lens sheets 35 and 36, respectively, isformed such that the same amount in a triangular shape is removedtherefrom by respective line segments (straight lines forming anapproximately 45° angle corresponding to respective two edges 33 a and33 b, 34 a and 34 b, 35 a and 35 b, and 36 a and 36 b) 33 c, 34 c, 35 cand 36 c extending between two edges 33 a and 33 b, 34 a and 34 b, 35 aand 35 b, and 36 a and 36 b defining the respective corner portions A.As a result, the respective corner portions A of the light guide plate33, the diffusing sheet 34 and the lens sheets 35 and 36 have a similarshape to each other and a sheet inversion detection portion is providedat each corner portion A (see FIG. 4A). In this connection, the lightguide plate 33, the diffusing sheet 34 and the lens sheets 35 and 36 maybe formed by actually cutting the corner portions A of sheet membersthat initially have a substantially rectangular shape along therespective straight lines 33 c, 34 c, 35 c and 36 c, or may be formed insheets 33, 34, 35 and 36 that are made in a shape in which the tips ofthe respective corner portions A are removed from the start using aforming die.

At a wall portion 32 b of the tray 32 at which the corner portions A ofthe light guide plate 33, diffusing sheet 34, and lens sheets 35 and 36are disposed, an opposing surface 32 c is arranged along the linesegments 33 c, 34 c, 35 c, and 36 c of the corner portion A so as tocorrespond to the shape of the corner portions A from which the tips areremoved. The opposing surface 32 c restrains the line segments 33 c, 34c, 35 c, and 36 c after the sheets are housed in the tray 32 (see FIG.4B). In this connection, the opposing surface 32 c is not provided atthe area of the wall portion 32 b at which the other corner portions(corner portions B, C and D, described later) of the light guide plate33, the diffusing sheet 34, and the lens sheets 35 and 36 are disposed(see FIG. 2 and FIG. 5).

Further, in the diffusing sheet 34 and the lens sheets 35 and 36,respectively, the tip of one corner portion (denoted by representativecharacter B in FIG. 3) among the corner portions other than the cornerportion A preferably has a shape in which it is trimmed off byrespective second line segments 34 e, 35 e, 36 e that extend between twoedges 34 a and 34 d, 35 a and 35 d, and 36 a and 36 d defining therespective corner portions B. The shapes of the second line segments 34e, 35 e and 36 e are different from each other among the adjoiningsheets 34, 35 and 36.

More specifically, with respect to the diffusing sheet 34, the tip ofthe corner portion B defined by the two edges 34 a and 34 d has a shapethat is trimmed by a straight line (second line segment) 34 e that linksthe two edges 34 a and 34 d. With respect to the lens sheet 35, the tipof the corner portion B formed by the two edges 35 a and 35 d has ashape that is trimmed by an arc (second line segment) 35 e thatprotrudes outward and links the two edges 35 a and 35 d. Further, withrespect to the lens sheet 36, the tip of the corner portion B formed bythe two edges 36 a and 36 d has a shape that is trimmed by a straightline (second line segment) 36 e that links the two edges 36 a and 36 d.As a result, a missing sheet detection portion is provided at the cornerportion B of the light guide plate 33, the diffusing sheet 34, and thelens sheets 35 and 36 (see FIG. 5).

The straight lines 34 e and 36 e that trim the tips of the cornerportions B of the sheets 34 and 36 are arranged so as to form angles ofapproximately 45° with respect to the two edges 34 a and 34 d, and 36 aand 36 d of the sheets 34 and 36, respectively, and the arc 35 e thattrims the tip of the corner portion B of the sheet 35 preferably has acircumference that is about ¼ the circumference of a circle of apredetermined radius, although the present invention is not limitedthereto. As shown in FIG. 5B, the diffusing sheet 34 and the lens sheets35 and 36 are preferably stacked in the order of sheets with thesmallest removed area (in other words, stacked in the order of sheetswith the largest remaining area), and the edge portions of the arc 35 eof the lens sheet 35 are linked by the straight line 36 e of the lenssheet 36 that is stacked thereon. In this connection, the tip of thecorner portion B of the light guide plate 33 is not trimmed off.

The area that is trimmed off by the second line segments 34 e, 35 e, and36 e at the corner portion B of the diffusing sheet 34 and the lenssheets 35 and 36 is smaller than the area that is trimmed off by theline segments 33 c, 34 c, 35 c, and 36 c at the corner portion A of thelight guide plate 33, the diffusing sheet 34 and the lens sheets 35 and36. Accordingly, when the corner portion B of each sheet is disposed atthe area defined by the opposing surface 32 c of the tray 32 where,originally, the corner portion A should be disposed, the corner portionsB of the diffusing sheet 34 and the lens sheets 35 and 36 and,naturally, the light guide plate 33 are arranged to come to a standstillon the opposing surface 32 c of the tray 32.

The diffusing sheet 34 and the lens sheets 35 and 36 may be formed byactually cutting off the corner portions B of sheet members thatinitially have a substantially rectangular shape along the respectivestraight lines 34 e and 36 e or the arc 35 e, or may be formed in sheets34, 35 and 36 that are made in a shape in which the tips of therespective corner portions B are removed from the start using a formingdie. The tips of corner portions C and D (see FIG. 3) of the light guideplate 33, the diffusing sheet 34, and the lens sheets 35 and 36 are nottrimmed off in any way.

The light guide plate 33, the diffusing sheet 34, and the lens sheets 35and 36 are stacked in order from the sheet with the smallest areatrimmed off at the corner portion B. The shapes of the second linesegments 34 e, 35 e and 36 e between the respective two edges 34 a and34 d, 35 a and 35 d, and 36 a and 36 d that define the corner portion Bof the diffusing sheet 34, and the lens sheets 35 and 36, respectively,differ between adjoining sheets. Therefore, when any sheet among thesesheets 33, 34, 35 and 36 that constitute a sheet laminated body ismissing, the alignment of the second line segments 34 e, 35 e and 36 ethat have different shapes gets out of order, and since this willimmediately look strange to a viewer upon visual observation, it ispossible to easily distinguish whether the respective sheets 33, 34, 35and 36 are sufficient or missing (missing sheet detection function).

Further, among the sheets that are adjacent to each other, with respectto sheets 34 and 36, the respective two edges that define the cornerportions thereof 34 a and 34 d, and 36 a and 36 d are joined by thestraight lines 34 e and 36 e, and with respect to the sheet 35, the twoedges 35 a and 35 d constituting the corner portion B thereof are joinedby a curved line (arc 35 e). Therefore, since the straight lines 34 eand 36 e and the curved line 35 e are adjacent, it is easy to discover amissing one of the sheets 34, 35 and 36.

Next, a function (sheet inversion detection function) that indicateswhen the light guide plate 33, the diffusing sheet 34, or the lenssheets 35 and 36 are disposed in an inverted condition will be describedbased on FIGS. 6A-6D and FIG. 7. When any member of the group includingthe light guide plate 33, the diffusing sheet 34, and the lens sheets 35and 36 is disposed inside the tray 32 in a condition in which the topsurface and the bottom surface thereof are in an upside-down state(inverted), the corner portion B or D of that inverted sheet will bemounted on an area at which the opposing surface 32 c of the tray 32 islocated where, originally, the corner portion A should be disposed. Whenthe corner portion B is mounted on the area where the opposing surface32 c of the tray 32 is located, as shown in FIG. 6, the corner portion Bof the inverted light guide plate 33, diffusing sheet 34, or lens sheet35 or 36 comes to a standstill on the opposing surface 32 c of the tray32, and by visually observing this state, it is discovered that thesheet in question is inverted. Further, when any member of the groupincluding the light guide plate 33, the diffusing sheet 34, and the lenssheets 35 and 36 is inverted and the corner portion D thereof is mountedon an area at which the opposing surface 32 c of the tray 32 is located,the corner portion D, from which the tip has not been removed, comes toa standstill on the opposing surface 32 c of the tray 32.

According to the present preferred embodiment, the tips of the cornerportions A of the light guide plate 33, the diffusing sheet 34, and thelens sheets 35 and 36 are preferably shaped such that they are trimmedoff by line segments 33 c, 34 c, 35 c and 36 c that extend between thetwo edges 33 a and 33 b, 34 a and 34 b, 35 a and 35 b, and 36 a and 36 bthat define the respective corner portions. Further, in the wall portion32 b of the tray 32, an opposing surface 32 c is arranged along the linesegments 33 c, 34 c, 35 c and 36 c of the corner portions A so as tocorrespond to the shape of the corner portions A from which the tips aretrimmed off. Therefore, since the configuration adopted is such that,when the light guide plate 33, the diffusing sheet 34, or the lenssheets 35 and 36 are housed in the tray 32 in a condition in which thetop surface and the bottom surface thereof are in an inverted state,(the tip of) another corner portion B or D comes to a standstill on theopposing surface 32 c, it can be easily discovered that the light guideplate 33, the diffusing sheet 34, or the lens sheet 35 or 36 is disposedin an upside-down condition. Further, since the configuration is one inwhich only the tip of the corner portion A of the light guide plate 33,the diffusing sheet 34, and the lens sheets 35 and 36 is trimmed off, itis possible to make the backlight apparatus 3 small without sacrificingthe active area of the light guide plate 33, the diffusing sheet 34, andthe lens sheets 35 and 36.

Furthermore, the configuration adopted is one in which, when the lightguide plate 33, the diffusing sheet 34, and the lens sheets 35 and 36are laminated and housed in the tray 32 such that a sheet inversiondetection portion is located at the corner portions A of the light guideplate 33, the diffusing sheet 34, and the lens sheets 35 and 36 and amissing sheet detection portion is located at the other corner portionsB, the missing sheet detection portion comes to a standstill on theopposing surface 32 c of the tray 32 when the light guide plate 33, thediffusing sheet 34, or the lens sheets 35 or 36 is housed in the tray 32in a condition in which the top surface and the bottom surface thereofare inverted. It is therefore possible to easily discover, via the sheetinversion detection portion, that the light guide plate 33, thediffusing sheet 34, or the lens sheet 35 or 36 is disposed in anupside-down condition. It is also easy to discover, via the missingsheet detection portion, that there is a missing item among the lightguide plate 33, the diffusing sheet 34, and the lens sheets 35 and 36.Furthermore, by adopting a configuration in which the display panel 4 isdisposed in front of the backlight apparatus 3, it is possible to make asmall liquid crystal display 2 and television receiver apparatus 1 inwhich it can be easily discovered that the light guide plate 33, thediffusing sheet 34, or the lens sheets 35 and 36 is disposed in anupside-down condition.

MODIFICATION EXAMPLES

Next, modification examples of preferred embodiments of the presentinvention will be described referring to FIGS. 8A-8F. In the figures, asquare formed by alternate long and short dashed lines represents acorner portion at which a sheet inversion detection portion is disposedand, likewise, a circle formed by alternate long and short dashed linesrepresents a corner portion at which a missing sheet detection portionis disposed. In modification example 1 shown in FIG. 8A, among the fourcorner portions of the light guide plate 33, the diffusing sheet 34, andthe lens sheets 35 and 36, a pair of sheet inversion detection portionsare provided at diagonally opposing corner portions, and a missing sheetdetection portion is disposed at one of the remaining corner portions.

In modification example 2 shown in FIG. 8B, among the four cornerportions of the light guide plate 33, the diffusing sheet 34, and thelens sheets 35 and 36, a pair of missing sheet detection portions aredisposed at diagonally opposing corner portions, and a sheet inversiondetection portion is disposed at one of the remaining corner portions.

In modification example 3 shown in FIG. 8C, among the four cornerportions of the light guide plate 33, the diffusing sheet 34, and thelens sheets 35 and 36, a pair of sheet inversion detection portions aredisposed at diagonally opposing corner portions, and a pair of missingsheet detection portions are disposed at the remaining corner portions.By adopting this configuration, by checking the corner portions at aminimum of two adjacent positions, it is possible to discover if thelight guide plate 33, the diffusing sheet 34, or the lens sheet 35 or 36is disposed in an upside-down condition or is missing, and furthermore,these checks can be easily carried out in a short time.

In modification example 4 shown in FIG. 8D, among the four cornerportions of the light guide plate 33, the diffusing sheet 34, and thelens sheets 35 and 36, a single sheet inversion detection portion and asingle missing sheet detection portion are disposed at diagonallyopposing corner portions.

In modification example 5 shown in FIG. 8E, missing sheet detectionportions are disposed at three of the corner portions among the fourcorner portions of the light guide plate 33, the diffusing sheet 34, andthe lens sheets 35 and 36, and a sheet inversion detection portion isdisposed at the remaining corner portion.

In modification example 6 shown in FIG. 8F, sheet inversion detectionportions are disposed at three of the corner portions among the fourcorner portions of the light guide plate 33, the diffusing sheet 34, andthe lens sheets 35 and 36, and a missing sheet detection portion isdisposed at the remaining single corner portion.

Further, in the above described modification examples 1 to 6, naturallythe opposing surface 32 c is disposed at the area of the wall portion 32b of the tray 32 at which the sheet inversion detection portion of thelight guide plate 33, diffusing sheet 34, and the lens sheets 35 and 36should originally be disposed.

The sheet inversion detection function relating to the abovemodification examples is the same as that of the above describedpreferred embodiments, and a description thereof is thus omitted.

OTHER PREFERRED EMBODIMENTS

The present invention is not limited to the preferred embodimentsdescribed by the foregoing description and drawings. For example, thefollowing preferred embodiments are also included in the technical scopeof the present invention.

(1) The optical sheets of the present invention include every kind oflight control sheet, such as a reflection sheet.

(2) The backlight apparatus according to the present invention is alsoapplicable to a display device other than a device that displays usingliquid crystal, such as a plasma display device or other type of displaydevice.

(3) The backlight apparatus according to the present invention is alsoapplicable to a side-light type backlight.

(4) A cold-cathode tube, a hot-cathode tube, and an electric dischargelamp can also be use as the light source of the backlight apparatus.

(5) A curved line may also be used for a line segment that is formed ata sheet inversion detection portion.

(6) A curved line other than an arc or a straight line for which anangle with respect to an outer edge of a sheet is other than 45° mayalso be applied for a line segment that is formed at a missing sheetdetection portion.

(7) The corner portions of the optical sheets may be configured by onlya sheet inversion detection portion and corner portions from which thetips are not trimmed off, without forming a missing sheet detectionportion.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A lighting device comprising: a tray including a wall portion; and anoptical sheet disposed inside the tray and including a first cornerportion, a second corner portion, and a third corner portion; whereinthe first corner portion and the third corner portion, both of whichinclude a trimmed portion, are provided at diagonally opposing cornerportions; the second corner portion does not include any trimmedportions; and the wall portion is arranged on the tray to oppose thetrimmed portion of the first corner portion.
 2. A lighting device ofclaim 1, wherein the trimmed portion of the first corner portion isdefined by a line extending from one side of the optical sheet to anadjacent side of the optical sheet.
 3. A display device comprising; thelighting device of claim 1; and a display panel.